Any light striking particles suspended in a liquid is scattered. The intensity of this light scattering is used in optical turbidity measurement as a direct measure for the determination of turbidity. Different measurement angles are used for different applications—in part due to national and local legal provisions and regulations. For example, 90° scattered light is used in drinking water applications, among others. Breweries often use a scattered light angle in the range of 11° to 25°. In measurements in sludges, a backscattering angle of >90° (e.g., 135°) is commonly used. “FNU” units (Formazin Nephelometric Units) are often used as reference measurement or for turbidity values.
Typically, a turbidity sensor based upon scattered light measurement can be illustrated as in FIG. 1. From the light source 1, transmission light 7 (solid line) is radiated through a window 6 that is transparent to the transmission light 7 into a measuring chamber 5. There, the light is scattered on particles in the medium 3 at a scattering point P at a measurement angle α or converted into reception light 8 (dashed line). Through a window 6 that is transparent to the reception light 8, the reception light arrives at a receiver 2 through, for example, an aperture 4. The light intensity arriving at the receiver 2 is a measure of the turbidity.
However, problems can occur in this process. Due to the optical windows 6 on both sides of the measuring chamber 5 and due to the active elements likewise on both sides of the measuring chamber 5 (such as electronic components, light source, receiver), the assembly of the turbidity sensor is complex and cost-intensive.
If several scattered light angles are to be measured using a single sensor, i.e., for example, 11° and 25°, or 90° and 180° and 11°, the problems described above are further exacerbated.